Mexico is the most populous Spanish-speaking country in the world and the second most-populous country in Latin America after Portuguese-speaking Brazil. About 70% of the people live in urban areas. Many Mexicans emigrate from rural areas that lack job opportunities -- such as the underdeveloped southern states and the crowded central plateau -- to the industrialized urban centers and the developing areas along the U.S.-Mexico border. According to some estimates, the population of the area around Mexico City is about 20 million, which would make it the largest concentration of population in the world. Cities bordering on the United States -- such as Tijuana and Ciudad Juarez -- and cities in the interior -- such as Guadalajara, Monterrey, and Puebla -- have undergone sharp rises in population.